1. Field of the Invention
This invention relates to a medical device, and more particularly, to a non-reusable syringe having an automatically retracting hypodermic needle which renders the syringe non-reusable after one use.
2. Background of the Art
Intravenous drug users have been identified as major vectors for the spread of AIDS in the general population because of sharing and reuse of hypodermic needles. With no vaccine in sight and reeducation lengthy and ineffective, a technological solution to discourage needle reuse is imperative. An additional consideration is that IV drug users obtain syringes primarily from the medical industry. Therefore, any device that reaches the drug-using community would also have to achieve acceptance in the health care field. The primary concerns of the health care industry are that new syringes 1) maintain the same capacity to hold fluids and allow for accurate incremental measurement of fluid as compared with standard syringes; 2) permit one-handed use so that the other hand of the health care worker is free to assist in holding the patient; 3) retract fully after use, thereby eliminating the possibility of needle sticks because of a mistaken belief the syringe has retracted fully when, in fact, it has not; 4) can clearly indicate prior use; 5) be extremely reliable even when used at a wide range temperature; 6) be easily assembled for mass production, and 7) be manufactured at an extremely low cost, due to the daily consumption of the product in quantities of millions of individual syringes, while maintaining a zero defect failure rate.
Various syringes with retracting or disarming technology have been devised in an attempt to address the needs of the health care industry. A number of different approaches have been used.
U.S. Pat. No. 4,747,831 to Kulli discloses a syringe-like cannula insertion set with a retraction needle. A manually releasable latch requires two-handed operation to release the needle after use. An IV drug user may simply not activate the manual release. Another example of a manually releasable needle in a safety syringe is U.S. Pat. No. 4,874,382 to Lindemann, et at., which also demonstrates the use of a "silo" to contain a retraction spring. The silo desirably protects the fluid from contact with the spring, but occupies volume which tends to undesirably increase the size of the syringe.
U.S. Pat. No. 5,064,419 to Gaarde combines a front-mounted retraction spring held against a yielding wall which must be flexed out of the way by the end of the plunger to allow retraction. Discrepancies in thickness or elasticity of the yielding wall can lead to release problems. Hang-ups can occur if the retraction spring catches the edge of the yielding wall during release. The device lacks a positive seal to prevent contact between fluid and spring. The seal depends upon pressure from the retraction spring and the quality of surfaces at the opening in the yielding wall.
U.S. Pat. No. 4,838,869 to Allard depends on flexing or breaking of clamps which are molded into the syringe or another part secured in the syringe and broken by the plunger. It also discloses a diaphragm in the plunger which must be penetrated by the needle and spring. These structures present serious quality control and assembly problems. Small broken off pieces can present a risk of hang-ups.
U.S. Pat. No. 4,994,034 to Botich, et at., illustrates a needle holder held by hooks in the front of the syringe and a frangible member molded across the front opening of the plunger, which has angled edges to spread the hooks. The hooks are molded as part of a front housing through which the needle passes. The housing is sealed to the syringe body with an "O" ring between the housing and syringe body. The fluid medication is free to contact the spring and spring holder. Outward lateral spreading of the hooked fingers is required to release the needle holder. The required flexing of the resilient fingers and hooks limit choice of materials and molding processes to achieve the right degree of elasticity without requiring excessive force to initiate retraction. Non-uniform flexing or breaking could lead to hang-ups. It is believed that molding the hooked housing would require molding with the aid of a collapsible core pin. Collapsible core technology tremendously increases mold cycle time, thus driving costs upward. The frangible piece on the end of the plunger must break readily and cleanly during retraction. Any jagged edges could catch the spring, causing jams. The degree of brittleness of the plunger material and dimensional control would make reliability difficult to obtain. A special seal for the needle is required at the tip to keep from drawing air into the fluid chamber and to prevent leakage.
U.S. Pat. No. 5,084,029 to Tagliaferri, et al., illustrates another approach using a frangible membrane on the plunger and a needle holder which can be hooked by a male hooking pawl which is held in the barrel by small shearing pins. The pins must shear upon application of sufficient force after hooking to allow the needle assembly to be withdrawn from the end of the syringe.
U.S. Pat. No. 5,053,010 to McGary, et al., is another example of a front-mounted retraction device which relies upon molding of structures which break or shear in order to provide a release. The front of the plunger shears through the piston, then breaks off part of the syringe body to release a spring-loaded needle holder. This creates obvious reliability problems in molding a body that will hold the compressed spring, yet break consistently without excessive effort. This device illustrates another potential problem in that failure of the syringe to fully penetrate through the head of the piston, yet breaking the needle-holding parts, could result in driving the needle forward into the patient's body at the moment of intended retraction.
The above-mentioned art illustrates the many attempts to produce a practical automatically retractable non-reusable syringe. The most commonly used syringes are 1 cc and 3 cc syringes which must be mass-produced at the rate of millions per day. The tiny needles are produced in the form of coiled tubing, and vary significantly from absolute straightness after they are cut to length. This alone leads to difficult assembly problems if the needle must be passed through a small opening. The extremely sharp tip of the needle will catch the edge of a hole and jam the production line. Any hope of high-speed production requires molds with 64 cavities or more to reduce unit cycle time. Therefore, molded structure within the barrel that requiring collapsing core pins such as are shown in some of the art mentioned are unlikely to be producible at competitive costs.
The gravity of the threat posed by AIDS and the fact that the main vector of the spread of the dreaded disease is through reuse of syringes by IV drug users has resulted in intense activity to develop the most practical, most reliable, easily assemblable, mass-producible syringe. A study of the problem reveals at least ten features that a retractable syringe should address in order to be a marketable product in quantities that could impact the spread of AIDS. A failure to address any one of these items could and has prevented the production of a practical retractable syringe. Such a syringe should:
1. Require only one inner contraction in the barrel so as to be formed by the separation of core pins at the kiss off point without the use of collapsible core technology. If collapsible core technology is required, the product can Be rendered noncompetitive due to production costs as a result of excessive cycle time.
2. The device should have a mechanism to prevent accidental retraction when the plunger is pushed all the way forward prior to drawing medications. This helps prevent accidental firing of the retraction mechanism. Syringes that accidentally "fire" and become useless during medical emergencies will never become accepted in the medical community.
3. Once the needle has been retracted, the device should be very difficult or impossible to reuse or reassemble for reuse.
4. The release mechanism should not require bending, flexing, or breaking of any release elements if the force applied by the thumb to initiate retraction is to be constant under various climatic conditions. Designs requiring breakage of parts for release create manufacturing and reliability problems when trying to achieve a very thin breakable membrane.
5. The needle must not advance even slightly forward at the retraction moment, for to do so drives it painfully into the patient.
6. The design must provide for easy assembly methods which do not require guiding the needle into small holes because presently manufactured needles, when epoxied into hubs or needle holders, are not perfectly aligned.
7. The design should not call for the use of minute parts that are delicate and drive up assembly costs while hampering reliability by increasing the risk of hang-ups during retraction.
8. The seals should be sufficient to prevent liquid leakage but must also prevent loss of vacuum. The biasing spring should be effectively sealed from the variable liquid holding chamber.
9. The amount of force required to initiate retraction should be predeterminable and not affected by creep of plastics or require the use of special plastic compositions.
10. The device should not be reusable if the plunger is sufficiently extended during the prior use to cause a retraction.
It would therefore be desirable to produce a practical syringe that meets these requirements. The syringe disclosed herein is the first mass-producible syringe suitable for use in a small size which meets all these requirements.